The demographic genetics of the Utah Mormon population will be studied using the 1.2 million-member Utah Genealogical Data Base. The genetic structure of 22 spatial subdivisions will be analyzed using migration matrix methods, isonymy, and pedigree studies. The results of these three methods will be compared in order to test the effects of their respective assumptions. Geographic distance, ethnic composition, and urban/rural composition will be treated as independent variables whose effects on genetic structure will be evaluated. An estimate of the maximum opportunity for natural selection in each subdivision will be calculated using a modified version of Crow's Index of total selection. All of these analyses will include assessments of temporal change. A major goal of this study is to use the knowledge gained from analysis of genetic structure to further our understanding of the prevalence, distribution, and evolution of genetic diseases. An initial effort in this direction will be an examination of the effects of parental consanguinity upon stillbirth frequencies, birth intervals, fertility, and prereproductive mortality. Case-control and cohort studies will be carried out to do this. The effects of confounding variables, such as socioeconomic status, will be controlled. Later, the distribution of specific genetic diseases will be studied, with special emphasis on the role of demographic genetics in determining spatial and temporal variation in genetic diseases.